Service manual

RC2000 Service Manual Chapter 4 Common RC2000 Questions 24
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1. A servo type polarization control device based on the Chaparral polarotor. The polarotor has a
three wire interface (5 volts DC, Pulse, and Return). The controller positions the polarotor by
sending a pulse width modulated (pwm) waveform to the polarotor. The off time of the waveform is
fixed at 15 to 20 milliseconds (msec) and the on time varies between 0.8 msec and 2.2 msec. As
the on time of the waveform changes the feed’s polarization angle varies over a range of
approximately 200 degrees. The servo type interface is completely open loop meaning that the
controller has no indication of what the polarotor’s actual polarization position is or if a polarotor is
even connected to the device.
2. The RC2000 can optionally control a rotating feed powered by a 24 volt DC motor (500 ma max)
that uses a potentiometer for position feed back such as the Seavey Engineering model ESA 124D
four port rotating feed. To support this option the RC2KPOL daughterboard must be installed in the
RC2000.
The user selects the polarization control device via the Rotating Feed Present CONFIG mode item. If
the item is set to 0 (NO) the controller assumes that it is interfaced to a polarotor type device. If the
item is set to 1 (YES) the controller assumes that it is attached to a rotating feed type polarization
control device.
If the controller is configured for use with a polarotor type device the controller’s internal representation
of any valid polarization position is a number between 293 (for a clockwise - CW - limit) and 956
(counter clockwise - CCW - limit). The user does not specify the limits for a polarotor type device.
If the controller is configured for use with a rotating feed type polarization control device the user must
specify the limits. The maximum possible range of polarization movement is 0 to 1023. For the
RC2000A the user sets the polarization limits via the POL LIMITS mode. With the RC2000C the user
sets the polarization limits via the CONFIG mode Rotating Feed CW Limit and Rotating Feed CCW
Limit items.
4.1.5 INVALID DATA ENTRY Error Message Due to Polarization Position Data
The INVALID DATA ENTRY message will be displayed anytime the user attempts to position the
antenna on a satellite and the polarization positions stored in the satellite’s non-volatile memory data
entry are outside the current polarization CW and CCW limits for whatever type of polarization control
the RC2000 is currently configured to support. As shipped from the factory, the default rotating feed
CW and CCW limits are 500 and the Rotating Feed Present CONFIG mode item is set to 0 (NO).
One case where this error can occur is if the user has specified a Seavey type rotating feed (via the
CONFIG mode Rotating Feed Present item) and does not have a feed or RC2KPOL daughterboard
connected to the controller. As shipped from the factory, the default rotating feed CW and CCW limits
are 500. If there is no rotating feed connected the controller’s sensed polarization position will be either
0 or 1023 and the controller will store either 0 or 1023 for the horizontal and vertical polarizations.
When the user programs a satellite into the controller’s memory via SETUP mode the controller DOES
NOT check to see that the polarization data is within the current polarization limits - the user will see
the SETUP mode DATA ACCEPTED message. However, when the user attempts to move (via AUTO
mode) to the satellite that has just been entered (via SETUP mode) the controller will display the
INVALID DATA ENTRY message because the current polarization CW and CCW limits are set to 500
(or some other values) but the satellite’s entry in non-volatile memory specifies that the horizontal and
vertical polarization positions are 0 or 1023.
Another case where this can occur is if the controller is configured for one type of polarization control
device, say a polarotor, when a satellite is programmed into non-volatile memory but the user later
changes the polarization control device (in this example to a rotating feed). If a polarotor is originally
specified when the data is stored in non-volatile memory the horizontal and vertical polarization values
stored for the satellite will be between 293 and 956. If the polarization control device is later changed
to a rotating feed device and the user attempts to recall the satellite, the polarization positions stored in
non-volatile memory may be outside the current polarization CW and CCW limits. This will again result
in the INVALID DATA ENTRY message being displayed.
It is not possible to edit an entry in non-volatile memory. The user can only delete (using DELETE
mode) or overwrite (via SETUP mode by specifying the name of a satellite which is already stored in
non-volatile memory) a satellite’s non-volatile memory entry.